The blood sugar concentration or blood glucose level is the amount of glucose (sugar) present in the blood of a human or animal. Normally in mammals, the body maintains blood glucose levels at a reference range between about 3.6 and 5.8 mM (mmol/L, i.e., millimoles/liter). When healthy, the body's homeostatic mechanisms keep blood glucose levels within a narrow range. Blood sugar levels can vary over the course of the day and spike after a meal, particularly after a sugar-rich meal. Moreover, certain medical conditions, such as diabetes, can interrupt the body's homeostatic mechanisms that maintain blood glucose levels within a narrow range, thus blood glucose levels may spike even further after a meal for a diabetic. Severe stress, such as trauma, stroke, myocardial infarction, surgery, or illness, can also impact a body's hemostatic mechanisms. High blood sugar levels can have a variety of adverse health effects, including weight gain, kidney damage, neurological damage, cardiovascular damage, and retina damage.